Recently, in a plate-making process of a printing plate for off-set printing, a CTP has been developed in which digital image data can be directly written in a light sensitive planographic printing plate material employing laser, and has been practically used.
Among them, a printing plate material comprising an aluminum support and provided thereon, an image formation layer are used in printing industries in which a relatively high printing durability is required.
As the aluminum support, an aluminum plate subjected to surface-roughening treatment and anodization treatment is generally used, however, when a large quantity of copies are printed employing a printing plate having such an aluminum plate, there are problems that a small dot image may be damaged or stain may occur at non-image portions.
As a printing plate material to solve the above problems, a printing plate material is proposed in for example, Japanese Patent O.P.I. Publication No. 2000-255177, which comprises a grained aluminum support, having protrusions with a specific average height consisting of boehmite on the surface, and provided thereon, a polymerizable light sensitive layer.
Known is a printing plate material comprising an aluminum support which is subjected to a specific surface-roughening treatment, anodization treatment, and then hydrophilization treatment employing polyvinyl phosphonic acid (see for example, Japanese Patent O.P.I. Publication No. 2002-103834), or a printing plate material comprising an aluminum support and a light sensitive layer, an intermediate layer containing polyvinyl phosphonic acid between the aluminum support and the light sensitive layer (see for example, Japanese Patent O.P.I. Publication No. 2002-57831). However, when a large quantity of copies are printed, there are some cases in the above printing plate material where a small dot image may be damaged or stain may occur at non-image portions. Therefore, the above printing plate material is not satisfactory in printing durability and anti-stain property.